In the parent application, Ser. No. 07/744,179, the present inventor disclosed and claimed a class of nonaqueous electrolyte solvent systems. It has since been discovered that if only two of such solvents are used, namely dioxolane and dimethoxyethane, and in particular proportions, this provides significant advantages that are surprising and unexpected.
Electrolytes comprising dioxolane and dimethoxyethane are known in the art, however prior artisans have not disclosed, or even suggested an electrolyte solvent system consisting essentially of a dioxolane-based solvent and a dimethoxyethane-based solvent in the particular proportions taught herein. U.S. Pat. No. 4,071,665 to Garth discloses a two component electrolyte solvent system containing dioxolane and dimethoxyethane in a ratio of 1 part dioxolane to 0 to 1 part dimethoxyethane such as at column 3, lines 9-10 and Example 6. However, Garth fails to describe or suggest an electrolyte solvent system containing dioxolane and dimethoxyethane in the novel ratios disclosed and claimed herein. U.S. Pat. No. 4,129,691 to Broussely describes electrolytes comprising two and three solvent components. Although Broussely describes an electrolyte having one part dioxolane to three parts dimethoxyethane as part of a solvent complex, such as at column 5, line 20, it is a three component solvent system and not a two component solvent system as in the present invention. Broussely also describes a two component solvent system of dioxolane and dimethoxyethane, such as at column 3, lines 39-40, however those solvents are in equal proportions to one another and not in the novel ratios disclosed and claimed herein. U.S. Pat. No. 4,489,144 to Clark discloses an electrolyte solution containing dioxolane and dimethoxyethane. However, that three component electrolyte utilizes a significantly greater amount of dioxolane than dimethoxyethane, such as in a ratio of one and one third to one, respectively, as noted at column 9, line 19.
Numerous applications for electrochemical cells require that the cell be capable of providing a current output of at least some minimal value over an extended period of time, referred to herein as its "discharge period". This is particularly desirable for applications involving portable consumer electronic products. Moreover, many applications for electrochemical cells require that the cell be capable of providing a current output with minimal reduction in voltage level, that is, that the cell output voltage have a minimal decay rate over the course of the cell discharge period. This is particularly desirable in high current drain applications such as camera flash applications. Prior artisans, including Garth, Broussely, and Clark, have entirely failed to recognize these and other advantages resulting from an electrolyte solvent system consisting essentially of a dioxolane-based solvent and a dimethoxyethane-based solvent in the ratios taught herein.
Currently known electrolytes containing dioxolane and dimethoxyethane have discharge periods of only moderate duration and relatively rapid voltage decay rates. It is desirable to provide a cell that has a significantly longer discharge period, and a voltage output that is relatively constant and not subject to such relatively rapid voltage decay.